Increasing evidence suggests that bronchial hyperreactivity in asthmatic subjects is caused by alterations in responsivity of airway smooth muscle to contractile or relaxant stimuli. The long-term objective of this project is to characterize the factors which regulate contractile and relaxant responses in canine airway smooth muscle and to examine the mechanisms by which the muscle's responsivity may change. The major goal of this proposal is to identify the mechanism of histamine's capacity to activate alpha-adrenergic mechanisms in canine trachealis, but the extent to which this phenomenon is important in other sites in the bronchial tree, as well as the effects of serveral other substances on responsivity of trachealis muscle, will also be tested. Specific aims are: 1. To compare histamine's effects on alpha-adrenergic mechanisms in smooth muscle of canine bronchi and trachea; 2. To characterize the optimal techniques for study of functional canine trachealis muscle cells in culture by use of pliable substrates for detecting contractions in isolated cells and by use of immunofluorescent techniques to detect contractile proteins in cells; 3. To characterize the relationships in cultured canine trachealis muscle cells between exposure of cells to histamine, depolarization of cell surface membranes, and activation of alpha-adrenergic responses; 4. To characterize the effects of histamine in cultured trachealis muscle cells on alpha-adrenergic receptors, activity of adenylate cyclase, and synthesis of prostaglandins in the cells; 5. To characterize the regulation of beta-adrenergic relaxant responsiveness in culture trachealis muscle cells by use of physiologic and pharmacologic techniques and by ultrastructural localization of beta-adrenergic receptors. 6. To examine the effects of other stimuli, such as substance P, endotoxin, and leukotrienes on physiologic and pharamacologic properties of culture canine trachealis muscle cells.